System for cooling material using co{11 {11 snow

ABSTRACT

High pressure liquid CO2 is expanded through nozzles to produce CO2 snow which is applied to the material being cooled. CO2 vapor is suitably connected, as through a check valve, to a location between the snow nozzle and a control valve therefor. Vapor pressure is regulated so that CO2 vapor will be immediately supplied to flush liquid CO2 from the conduit leading to the snow nozzle whenever snow-making is halted. When an insulated cooling enclosure is used, as in a food freezer, a continuous flow of CO2 vapor is maintained through the nozzles sufficient to prevent the entry of ambient air into the enclosure when snow-making is temporarily halted.

United States Patent [191 Tyree, Jr.

[ June 11, 1974 I 1 SYSTEIVI COOLING MATERIAL USING co SNOW [76] Inventor: Lewis Tyree, .Ir., 10401 S. Oakley Ave., Chicago, 111. 60643 [22] Filed: Jan. 27, 1972 [21] Appl. No.: 221,212

Related U.S. Application Data [63] Continuation-impart of Ser. No. 14,575, Feb. 26,

1970. Pat. No. 3,672,181.

'52 us. Cl 62/62, 62/384, 62/514 [51] Int. Cl. F25d 25/03 [58] Field of Search 239/25; 62/62, 386, 388, 62/614, 513, 384

[5 6] References Cited UNITED STATES PATENTS 2.496.816 2/1950 Shlumbohm 62/514 X 3.001.374 9/1961 Hutton, .lr 62/514 X 3,109,296 11/1963 Williamson et al. 62/514 X 3,435,632 4/1969 Fallin 62/380 X 3,661.483 5/1972 Bose 62/384 X FOREIGN PATENTS OR APPLICATIONS 1.119.650 7/1968 Great Britain 62/384 Primary ExaminerMeyer Perlin Assistant Examiner-Ronald C. Capossela Attorney, Agent, or FirmFitch, Even, Tabin & Luedeka [5 7] ABSTRACT High pressure liquid CO is expanded through nozzles to produce CO snow which is applied to the material being cooled. CO vapor is suitably connected, as through a check valve, to a location between the snow nozzle and a control valve therefor. Vapor pressure is regulated so that CO vapor will be immediately supplied to flush liquid CO from the conduit leading to the snow nozzle Whenever snow-making is halted. When an insulated cooling enclosure is used, as in a food freezer, a continuous flow of CO vapor is maintained through the nozzles sufficient to prevent the entry of ambient air into the enclosure when snowmaking is temporarily halted.

, 16 Claims, 3 Drawing Figures I46 Ho 3 F 2 PR l P v I476 135 m {g} [Mb 7k u 395 I529 l PATENTEDJUN 1 1 \914 SYSTEM FOR COOLING MATERIAL USING CO SNOW This application is a continuation-in-part of my application Ser. No. 14,575, filed Feb. 26, 1970 now U.S. Pat. No. 3,672,181.

This invention relates to carbon dioxide refrigeration systems and more particularly to methods for cooling material using carbon dioxide snow and to apparatus for carrying out such cooling.

Mechanical refrigeration units, including those of the air blast type, have long been employed for cooling and freezing articles. More recently, systems employing cryogenics particularly liquid nitrogen, have entered the commercial market. Solid carbon dioxide is considered to be excellently suited for use in cooling material because it exhibits the advantage of exceptional weight efficiency, plus a temperature which is much closer to the freezing point of water than is liquid nitrogen.

Various systems have been developed to utilize the refrigeration advantages of carbon dioxide, but many have exhibited drawbacks. Some of these systems have employed a grinding operation wherein large blocks of solid carbon dioxide are reduced to a granular size for the ultimate refrigeration operation, and such systems are considered to be inherently inefficient, giving rise to additional loss of refrigeration capacity by the sublimation which occurs during the grinding operation. lm proved systems for the utilization of carbon dioxide for cooling material continue to be desired.

It is an object of the present invention to provide improved systems for using liquid carbon dioxide to cool material. Another object is to provide improved methods of cooling material by flashing high pressure liquid carbon dioxide to deposit carbon dioxide snow directly upon the material, which methods can be operated intermittently if necessarywithout undesirable effects. A further object is to provide efficient troublefree apparatus for continuously or intermittently flashing liquid carbon dioxide to snow for deposition upon material being cooled. These and other objects of the invention should be apparent from the following detailed description of systems embodying various features of the invention when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic view of a refrigeration system embodying various of the features of the invention designed to cool material which'is moved horizontally along a conveyor;

FIG. 2 is an enlarged view of one of the snow nozzles shown in the system illustrated in FIG. 1; and

FIG. 3 is a fragmentary view of an alternative system similar to that shown in FIG. 1.

A refrigeration system 110 is diagrammatically illustrated by an insulated enclosure 111 into which material 113 being cooled or frozen enters through an entrance 114 and is carried therethrough on a moving conveyor 115 to an exit 116. Liquid carbon dioxide under high pressure is expanded through two groups of snow nozzles 117a and 11712 to create showers of snow within the enclosure 111. Each group may include three or more snow nozzles, and the group of nozzles 117a are directed toward the advancing material 113 while the group of nozzles 1l7b are pointed in the general direction of travel of the material. Additional snow nozzles (not shown) may be provided near the entrance 114 to the enclosure if desired for handling a particular product. Efficient deposition of snow is accomplished zxaaaa re iquisi C01 aeliss atiairtxh samss,

sure. Baffles or chutes 119 are used to assure that the QQZSEOW from both of the gro llis of snow nozzles 117 is directed downward to the material being cooled. The snow nozzle operation is adjusted to assure that there i Cqjaaqrszsi iaa r m 29th th 99252911139295- exit 116 of the enclosure 111 to prevent the entry of humidity-bearing ambient air.

The snow which falls to the bottom of the enclosure 111 comes to rest upon a lower, hollow heat-exchange plate 123 located in the region below the snow nozzles l 17. The cooling capacity of this snow is recovered and is employed to precool the high pressure liquid carbon dioxide flowing toward the nozzles 117, thereby increasing the percentage of snow created at the expansion nozzles while obviating a potential problem of excessive snow build-up as a result of extended duration of operation. Temperature control within the enclosure 111 is maintained by appropriately reading the temperature therewithin and changing the effective area of the orifices within the snow nozzles 117 to either increase or decrease the amount of snow created, as explained hereinafter in detail. As a result, the illustrated system 110, which is designed to operate as a freezer, provides fast, efficient freezing of material 113 and is well adapted to handle a fairly high capacity of material flow therethrough.

More specifically, a standard carbon dioxide liquid storage vessel 125 is employed which is designed for the storage of liquid carbon dioxide at about 300 psig. and 0F. An accompanying refrigeration unit 127, such as a freon condenser, is associated with the storage vessel 125 and is designed to operate continuously, if necessary, to condense carbon dioxide vapor in the vessel and maintain a temperature close to 0F. The capacity of the refrigeration unit 127, which is a well known device often used for this purpose, is determined by the operating conditions of the overall installation. It may, for example, be designed to condense about 50 pounds of liquid carbon dioxide an hour at about 300 psig., which thus provides a condensation capacity of some 1200 pounds of carbon dioxide per day.

A line 129 connects the liquid phase of the storage vessel to one side of a heat-exchanger 131. Depending upon the distance between the storage vessel 125 and the point of end use, it may be desirable to include a suitable pump (not shown) to provide hydraulic head for creating a circulation flow of high pressure liquid C0 throughout the system and back to the storage vessel 125.

The heat-exchanger 131 subcools the high pressure iqu 09 lsa ias. bcstorase 19 x125. in? mains; described more fully hereinafter. By subcooling the high pressure liquid, a greater percentage of liquid CO is transformed into snow at the expansion snow nozzles 117. If desired, even more efficient snow-making is car- .ufsslquthy ur er u ql atheliaLQgz by placing an additional heat-exchange unit 132 in thedhie 133 Y leaving the heat-exchanger 131. The heat-exchange unit 132 splits a portion of the liquid CO from the main flow in the line 133 and expands it into the shell sfie of the heat-exchanger to provide a pool of low temperature liquid and vapor; the vapor is withdrawn compressed, cooled and returned to the storage vessel 125 through a suitable line (not shown). The temperature of the main stream of liquid C0 may be reduced to as low as about 50 or 60F. This subcooled liquid carbon dioxide exits from the heat-exchange unit 132 and flows through a line 134 to a tee connection 135. A pair of lines 137a and 137b are connected to the tee 13S,

and each contains a pressure regulating valve 139a and 13%. On the downstream side of the pressure regulating valves, additional tee connections 141a and 141!) are provided, one leg of each of which leads to a manifold 142a, 142b which supplies the respective: group of snow nozzles 1170, 11711. As indicated above, each manifold 142 supports a plurality of nozzles 117 spaced across the width of the enclosure 111 so that a relatively uniform snow pattern is deposited across the entire width of a conveyor belt.

Connected to the other legs of the tees 141a and 1411: are a pair of vapor lines 143a, 143b which are joined to a common line 145 leading back to the vapor section of the storage vessel 125. Check valves 147a and l47b are disposed in the lines 143a and 143b to allow flow only out of the vessel and through the lines to the tees 141 and prevent flow in the opposite direction. Both of the lines 143a and 143!) also contain pressure regulators 146a and 146b. The purpose of the vapor lines 143a,143b is explained in detail hereinafter.

-The enclosure 111 is constructed so that the conveyor 115 carrying the material 113 to be cooled or frozen passes generally centrally therethrough. The snow nozzles 117 are located near the top of the enclosure 111 and are preferably positioned to direct showers of snow. downward and at an angle to the conveyor. The nozzles 117 are constructed so as to open only when the liquid carbon dioxide being supplied to the manifold reaches a certain minimum pressure, the enclosure 111 being at substantially atmospheric pressure. The specific construction of the nozzles 117 is explained in detail hereinafter. Generally, the higher the pressure at which the nozzles 117 are operated, the finer are the particles of snow which are created, and fine snow may be preferred when cooling certain material.

Although ancillary blowers might be positioned within the enclosure so as to increase the circulation therewithin, satisfactory performance is obtained without the use of such blowers, thus removing a possible maintenance problem from the apparatus. Moreover, pivotable baffles or dampers (not shown) might be located generally adjacent each group of snow nozzles 117 to aid in directing gas flow; however such dampers are not generally considered necessary. Preferably the vapor flow pattern created during normal operationis such as to havea moderate leakage of CO vapor out the discharge o r eitit end 116 of the enclosure, whiTe" the major portion of the vapor escapes from the entrance end 114 of the enclosure and thus carries out some pre-chilling of the material 113 before it reaches the snow section of the apparatus. As earlier indicated, if desired for certain applications, a pre-snowing may also be effected adjacent the entrance 114 by adding an additional group of snow nozzles which will deposit an initial thin coating of snow upon the material entering the enclosure 111.

No matter how efficient the design may be for depositing the snow on top of the material 113 passing along the conveyor belt, it must be realized that some snow will fall past the belt and reach the bottom of the enclosure 111. The hollow heat-exchange plate 123 is provided in the snowing region of the enclosure to handle this snow. A suitable heat-exchange fluid, such as a Freon, is provided in the hollow plate 123 and the associated heat-exchanger 131 so as to recover the cooling capacity of this snow and to prevent excessive build-up of snow at the bottom of the insulated enclosure 111.

Sufficient circulation of the heat-exchange liquid through the hollow plate 123 and through a coil within the heat-exchanger 131 is accomplished through natural convection so a circulating pump is not needed.

Moreover, a freon can be chosen which boils below the temperature of the liquid CO entering the heatexchanger 131 to further promote circulation. A sole noid operated shut-off valve 149 is provided in the line leading from the hollow plate 123 to the heatexchanger 131. The solenoid valve 149 is connected to a control mechanism 151 which may be a part of another controller 153 for regulating the pressurereg ulating valves 139 supplyi rgthe liquid CO to the snow nozzles. The control mechanisin 151 is setto close the solenoid shut-0E valve 149 at anytime when liquid CO is not being supplied to the snow nozzles 1- Qpsrat qn in this n a! m t/ ms (1 @5191 Q0; within the heat-exchanger 131 from turning solid-The construction of the heat-exchanger 131 has a central vertical tube through which the high pressure liquid CQ2 ,flows with th hsrein h fr .s rsu stss, surrounding the tube and the assembly being potted in aluminum or some other good heat-conducting material. Consequently, with the valve 149 closed there is not sufficient cooling capacity in the residual freon in the Coil to freeze q CQg-AternssratumssnsorlS. may be provided in the line 133 adjacent the exit from the heat-exchanger 131 and connected to the control mechanism 151 to close the valve 149 if the temperature of high pressure liquid flowing through the line 133 nears the freezing point. Such a temperature sensor 154 would be provided if automatic shut-off of the pp y of qu is notiss id if an insta la ion had a unit similar to the heat-exchange unit 132 already located adjacent the storage vessel so that the liquis CQZ ente n the hsa iesqhaaserll w sldhs at a lower temperature.

Control of the snow-making operation is facilitated greatly by employing snow nozzles 117 which have variable orifices. By increasing the effective area of the orifice, a significantly larger quantity of liquid will be flashed to snow and vapor than if only the pressure of the feed liquid were changed. Conversely, by decreasing the effective area of the orifice, the amount of snow which is created is quickly decreased. A suitable temperature sensor 161 is appropriately located within the insulated enclosure 111 to monitor the vapor temperature therewith and control the amount of snow created. if the temperature drops below the desired level, the effective area of the orifices in the snow nozzles 117 are decreased in order to reduce the amount of snow which is being created. On the other hand, if the vapor temperature within the enclosure 111 rises above the desired value, the effective orifice area is increased in order to create more snow.

in the illustrated embodiment, the snow nozzles 117 are constructed so that the effective area of the orifice changes as a direct result of the change in the liquid pressure on the feed side of the orifice. This feed pressure is regulated by the pressure-regulating valves 139a and 13% which are operated by the control mechanism 153 that responds to the temperature sensed in the enclosure 111 by the sensor 161. All of the nozzles, for example the nozzles 117a, attached to one manifold are set to open at the same pressure.- However, the two groups of nozzles 117a and 1171) may be set to open at different pressures, if desired, for regulation of snow deposition. When the control mechanism 153 causes the valves 139a, 13% to apply liquid CO2 pressure to the manifolds above the preset pressure, snowing begins; and further increases in the liquid pressure in the manifolds (and thus at each of the snow nozzles 117) causes the intensity of the snowing to increase. Increase in liquid CO pressure coupled with change in effective orifice size results in fast and substantial changes in the amount of snow that is created in the enclosure 111.

The illustrated nozzle design not only provides excellent regulation of the flow rate of liquid CO through As indicated above, the liquid C0 pressure on the feed side of the nozzles 117 is employed to effect the desired regulation of the orifice openings although other more sophisticated mechanism might be used. One form of suitable nozzle design is shown in FIG. 2. The individual nozzles 117 each have a housing 179 which has a circular orifice 181 formed in its lower wall. The housing 179 is supported from and rigidly connected to the liquid supply manifold by a side coupling 183. The sidewall of the housing 179 provides a hollow chamber above the orifice 181 which is circular in cross section. The upper end of the housing 179 is open to provide an opening through which a cylindrical plug 185 extends. The plug 185 has a suitable bottom end proportioned to close the orifice 181.

The upper end of the plug 185 is disposed in a support cap 187 which is connected via a bellows 189 to the upper portion of the housing 179. A tension spring 191, which has its upper end surrounding a seat provided on the support cap 187 and its lower end surrounding a seat provided on the upper end of the housing 179, biases the support cap toward the housing thus seating the lower end of the plug 185 in the orifice 181. The tension spring 191 is wound with a pre-load to prevent any relative movement between the plug 185 and the orifice 181 until a certain minimum pressure is reached.

in the illustrated embodiment, connection between the plug 185 and the support cap 187 is made adjustable by providing a threaded hole in the support cap 187 and providing mating threads on the exterior surface of a collar 193 keyed to the upper portion of the plug. Connection in this manner facilitates simple adjustment of the pressure at which the nozzle 117 will initially open. For example, by slotting the upper end of the plug 185, it can be rotated relative to the support cap 187 by a screwdriver and thus increase or decrease the tension on the pre-loaded spring 191 which biases the plug into seating position to close the orifice 181. Thus, the nozzles 117 will remain closed until the pressure in the hollow interior of the housing 179 and bellows 189 is sufficient to overcome the biasing of the spring 191. When this occurs, the support cap 187 moves slightly away from the housing 179, extending the bellows 189 and raising the plug so as to provide an annular opening between the perimeter of the orifice 181 and the bottom surface of the plug 185. The distance which the plug 185 moves away from the orifice 181 is dependent upon the amount of pressure in the manifold, which pressure, as was previously indicated, is regulated by the valves 139.

the nozzles, but it also prevents clogging of the nozzles because it assures that there is no substantial build-up of solid CO2 on the feed side of the orifice 181 during normal operations. For example, if some ancillary valve were used to shut off the flow of liquid CO2 to a fixed orifice when it was desired to halt snow-making, the liquid in the manifold 142 and in the nozzles would change to solid CO2 in situ when-the pressure reached a certain level. However, in the present situation wherein the apparatus is operated as a freezer, if thenozzles 117 are set to close the orifices 181 at about 150 p.s.i.g., for example, the high pressure liquid remaining in the manifold 142 may freeze if it gives up sufficient heat to the cold environment within the freezer enclosure 111 before snowing operation is again begun. The injection of CO vapor supplied through the lines 143a and 143b is used to obviate such an occurrence. I

Carbon dioxide vapor at a pressure of approximately 300 p.s.i.g. is available in the storage vessel 125. This vapor pressure is transmitted via the line 145 and is always available at the check valves 147a and 1471) in the lines 143a and 1431;, may be set to supply CO2 vapor to The pressure regulators 146a and 146b, disposed in the lines 143a and 143b, may be set to supply C0 vapor to the manifolds 142 at a pressure just a few pounds above that at which the nozzles 117 are set to close. Inasmuch as this vapor pressure will be well below the normal liquid pressure being supplied when expansion of high pressure liquid for the creation of snow is occurring, there will be no flow through the lines 143 because the check valves 147 will be held closed by the higher liquid pressure at the tees 141. However, when the control mechanism 153 actuates the pressure-regulating valves 139 to decrease the liquid CO pressure preparatory to halting snow-making by lowering the liquid CO2 pressure below the predetermined minimum pressure at which the nozzles are set to close, the flow of vapor through the lines 143a and 143b becomes important.

As soon as the liquid pressure at the tees 141 drops below the vapor pressure supplied by the pressureregulators 146, the check valves 147 will open thus either preventing the orifices 181 from being closed or immediately reopening them. The vapor will flush the liquid CO remaining in the manifolds 142 and the nozzles 117 out of the conduit network while maintaining relatively high pressure on any liquid CO2 trapped adjacent the downstream side of the pressure-regulating valves 139 which may be closed completely. Moreover, by maintaining a very slow flow of vapor through the manifolds 142 and out the nozzles 117 until snowmaking is again called for by the control mechanism 153, or until the apparatus is tobe shut down for a substantial length of tifnefthe possibilitytliat C O vapor in the manifolds 142 may be condensed to form CO snow is positively guarded against.

If all of the nozzles 117a and ll7b are set to operate at the same pressure, then only a single vapor pressureregulator 146 need be provided at a location in the line 145 before it branches. In the illustratedembodiment, separate pressure-regulators 146a and 14611 are provided so that the vapor supplied to each manifold 142 can be adjusted separately to a value slightly above that at which the nozzles 117a and 117b are set. The vapor is usually supplied-at a pressure of about 5 to about 15 7 p.s.i., preferably about l p.s.i-. greater than that at which the nozzles are set to close, although greater pressure can be used, so long as it is below the lowest pressure at which it will be desired to make snow. 7

As an alternative to setting the vapor pressureregulators 146 to a value slightly above the preset minimum pressure so as to cause the nozzles to remain slightly open, the same objective can be accomplished by providing a groove or depression in either the plug 185 or the orifice 181 seat so as to prevent a complete seal and allow a very slight amount of fluid passage when the nozzle is otherwise closed. With this arrangement, the pressure-regulator 146 can be set at a lower pressure, for instance 75 p.s.i.g. In FIG. 2, a shallow groove 195 is indicated on the surface of the lower end of the plug 185 through which fluid may pass when the plug 185 is seated in the orifice. Each pressureregulator 146 for the vapor is set slightly above the triple point pressure (preferably at at least about 80 p.s.i.a.) and thus maintains substantially that pressure in the line 143 and the manifold 142, preventing the liquid CO from'turning solid. The liquidCO will be slowly flushed out of the manifold through the grooves 5 y e p tp s ts- After a l Qfths isiy dfiQz. is flushed from the manifold, it is kept clear by maintaining a slow flow of CO2 vapor therethrough.

As a result of this arrangement, even if the environment of the insulated enclosure 111 wherein the nozzles 117 and their supporting manifolds 142 are disposed remains at a very cold temperature, as would be the case in a freezing apparatus where some build-up of snow had occurred, the manifolds leading to the nozzles remain free and clear and the possible condensation of vapor to form solid CO2 is positively prevented. Accordingly, the vapor pressure system is found to complement the illustrated snow nozzles which provide for efficient creation of CO snow and obviate any potential problem of blockage during normal operation. If such a controlled passage of vapor through otherwise closed snow nozzles is used, the vapor pressure is set to inject sufficient vapor into the enclosure to maintain a slow toward flow through the entrance 114 and the exit 116 to prevent the inflow of ambient air.

When operation of the refrigeration system is ready, the conveyor drive motor is actuated and the temperature control by the sensor 161 is initiated. Snowmaking results, and snow which falls to the bottom of the enclosure onto the hollow plate 123 is caused to sublime by taking up heat from the heat-exchange fluid circulated therethrough. This subcools the high pressure CO2 being fed to the snow nozzles 117 and results in a more efficient expansion by transforming a greater percentage of the high pressure liquid to CO snow. Whenever, snow-making ceases, the residual high pressure liquid in the manifolds 142 leading to the nozzles 117 is removed by flushing with to vapor fed thereinto from the storage vessel 125. Thus, troublefree operation is obtained in the apparatus even though some unforeseen delay, for example, in the availability of the product to be cooled or frozen, causes the apparatus to idle for a substantial period of time.

Modifications to the illustrated embodiments as would be obvious to one having the ordinary skill in the art are considered as falling within the scope of the invention which is defined by the claims appended hereto. For example, if the expense of automatic temperature control is not considered justifiable for a particular installation, the temperature at an appropriate location in the enclosure 111 may be visually read and the pressure-regulating valves I39 manually adjusted to maintain the desired temperature. In such an instance a separate solenoid shut-off valve might be included in th l sv q 992 Supply line to whish th 1395 ausa valve 149 can be interconnected, or reliance can be placed upon the sensor 154 in the exit line from the heat-exchanger 131.

Furthermore, it is believed that certain features of the invention are applicable to a system for cooling or freezing material where, instead of using snow nozzles 117 that employ orifice means biased to the closed position such as shown in FIGS. 1 and 2, standard snow l o rns a e used for the expansion of the liquid C0 Shown in FIG. 3 is such an alternative ernbodiment'of a snow-making system which might be substituted for that shown in FIG. 1 or which might be employed in apparatus of this general type for cooling material by the application of carbon dioxide snow. A standard snow horn 201 having a central fixed-orifice nozzle 202 is connected to a conduit 203 which supplies high pressure liquid carbon dioxide to the horn 201 for expansion into .COl snow hisk. is sted. tbwswat hxths horn onto the material being cooled. Although only a single snow horn 201 is shown, it should be understood that a plurality of snow horns could be used by interconnection to a common manifold.

The flow of liquid carbon dioxide to the snow horn is controlled by a simple open-shut control valve 204 (for example, a ball valve), which may be solenoidoperated and thus controlled remotely via a line 205 connected to a control mechanism 206, such as the temperature-operated mechanism 153 shown in FIG. 1. A tee 207 is connected into the liquid supply line 203, and a branch conduit 208 leads from the tee 207 to a check valve 209. A conduit 210 leading from the check valve is branched and one leg leads to an accumulator 211 while the other leg leads to an open-shut control valve 212. A conduit 213 at the inlet side of the control al e lea s soars? Of va qua s @52 9. liquid carbon dioxide storage vessel shown in FIG. 1. The valve 212 is connected by a line 214 to the control mechanism 206 used for stopping and starting the 92 1 f .lil li Q tqthswow 129 When it is desired to deposit snow onto material to be cooled which is located or being conveyed below the snow horn 201, the control mechanism 206 actuates the control valve 204, causing it to open and connect the conduit 203 to the source of high pressure liquid CO thus supplying liquid CO to the snow horn 201, Expansion of the high pressure liquid through the fixed orifice noule 202' creates snow and vapor, and the horn directs the snow downward against the material being cooled. At the same time as the control mechanism 206 opens the valve 204, it simultaneously opens he v lve ht s at tspn s ina some of 2 vapor and the accumulator 211 whereby it will be filled to its capacity. A pressure-regulator 215 is included in the CO2 vapor supply line so that the vapor pressure can be set to be less than the pressure of the high Press re l q d 0 n hssqnquitzqi-m 1,

Accordingly, whenever the valves 204 and 212 are both open, CO vapor pressure will be available at the check valve 209 but the checlcvalvew illbe held shut by the higher CO2 liquid pressure in the conduit 203.

However, the instant that the valve 204 is closed, the

check valve 209 immediatelyopens, causing CO vapor to flow through the line 208, through the tee 207 and out the orifice 202 in the snow horn. ln the illustrated embodiment in FIG. 3, the valve 212 closes at the same time as the valve 204, and the accumulator 211 holds a sufi'icient amount of CO vapor to assure that it will cause all of the liquid CO. on the downstream side of the valve 204 to be drained and flushed from the 601iduit 203. As an alternative to the inclusion of the accumulator 21 l, a time-delay circuit could be built into the controller 206 and thus simply leave the valve 212 open after the closing of the valve 204 for a sufficient duration of time to similarly assure that all of the liquid CO downstream of the valve 204 is drained and flushed from the conduit 203 by the flow of CO vapor.

The system illustrated provides troublefree operation because of the immediate availability of the CO flushing vapor at the check valve 209 so that the instant the liquid CO in the conduit203 between the valve 204 and the horn 201 begins to reflect the drop in pressure by the closing of the valve 204, the check valve 209 opens to apply vapor pressure to maintain pressure on the liquid CO2 and to expel it before it has the opportunity to be transformed to solid C The pressureregulator 215 is desirably set to supply CO vapor at a pressure well above the critical value (about 75 p.s.i.a.) below which solid transformation occurs, and preferably the CO2 vapor pressure at the check valve 209 is maintained at between about and about 50 p.s.i. below the pressure at which the CO snow horn l is operated. As a result, an efficient, troublefree system is provided which utilizes standard snow horns to deposit CO2 snow on the material bein g cooled.

Various of the features of the invention are set forth in the following claims.

What is claimed is: I

l. A method for cooling material using carbon dioxide, which method comprises supplying high pressure liquid C0 through a line which leads to snow nozzle means having orifice means biased to a closed position @1 2,.sm msaiibimms rsliauuiQ zth smh. the orifice means in the snow nozzle means to create CO snow and applying said CO snow to the material being cooled, halting said creation of CO snow by reducing the pressure of said high pressure liquid CO; being supplied to the snow nozzle means below that pressure at which the orifice means is biased to close, and automatically applying CO vapor to the snow nozzle means upon said reduction in liquid pressure and maintaining CO vapor flow through the orifice means.

2. A method in accordance with claim 1 wherein said snow nozzle means is mounted within means defining an enclosure, wherein the material being cooled is moved through the enclosure and wherein CO vapor is caused to flow through the orifice means into the enclosure in an amount sufficient to preclude the entry of ambient air into the enclosure.

5. Apparatus for cooling material using CO snow, which apparatus comprises snow nozzleifieahs having an rifi e thtquah which g PI$5 I liquid C02 is panded to create CO; snowandvzgaor, said snow nozzle means having plug means which is biased to physically close said orifice when the pressure of liquid CO at said snow nozzle means drops to a predetermined minimum value, means locating said snow nozzle means within an insulated enclosure into which material to be cooled is supplied by conveying means so the CO snow created is deposited upon the material being cooled, first conduit means for connecting said snow nozzle rneans to a source of high pressure liquid CQ first valve means disposed in said conduit means effective to qlatsfiiqilow nqazlsms nsfr Said q id c0. source, means for operating said first valve means to halt the creation of CO snow, second conduit means iogconnecting a source of CO2 vapor to said first con duit means at a location between said first valve means and said orifice, and check valve means in said second conduit means for automatically and immediately supplying CO2 vapor to said first conduit'means between said fir s t valve means and said orifice upon halting of CO2 snow creation to remove liquid CO therefrom by flushing with CO2 vapor.

6. Apparatus in accordance with claim 5 wherein said second conduit means contains pressure-regulator means set to supply CO vapor at a pressure above said predetermined minimum pressure but below the lowest pressure at which liquid CO2 will be supplied to said nozzle means during snow-making.

7. Apparatus inaccordance with claim s wh erein said orifice-plug means combination does not seal completely and permits a slow passage of CO through saiifi lcs l u iielvsm ansis in elgsed n qn.

8. Apparatus in accordance with claim 5 wherein said snow nozzle means is mounted within means defining an enclosure for cooling the material, wherein means is provided for moving the material to be cooled through said enclosure and wherein pressure-regulator means connected to said second conduit means supplies CO vapor at pressure to introduce a sufficient amount of CO vapor into said enclosure to preclude the entry of ambient air into said enclosure.

9. Apparatus in accordance with claim 8 wherein means is provided for sensing the temperature within said enclosure, wherein said first valve means is a pressure regulating valve, and wherein control means is provided connecting said sensing means and said first valve means for changing the pressure of the liquid CO2 supplied to said snow nozzle means in response to the temperature sensed within said enclosure. r

10. Apparatus in accordance with claim 5 wherein closing said first and second valve means at the same time when it is desired to halt snow-making.

13. Apparatus for cooling material using CO snow, which apparatus comprises snow nozzle means having an orifice through which high pressure liquid CO is expanded to create CO snow and vapor, plug means for automatically closing said orifice to flow of CO therethrough when the liquid CO pressure at said snow nozzle means reaches a predetermined minimum value, means locating said snow nozzle means so the CO snow is deposited upon material being cooled, first conduit means for connecting said snow nozzle means to a source of high pressure liquid CO first valve means disposed in said conduit means effective to reduce the pressure of the high pressure liquid CO below said predetermined minimum pressure to thereby halt the creation of CO snow, second conduit means for connecting a source of CO vapor to said snow nozzle means, and means for automatically supplying CO vapor to said snow nozzle means in fluid communication with said orifice at the time of halting the CO snow creation.

14. Apparatus in accordance with claim 13 wherein said snow-nozzle means is mounted within an insulated enclosure for cooling the material and wherein means is provided for moving the material to be cooled through said enclosure.

15. A method for cooling material using carbon dioxide, which method comprises supplying high pressure liquid CO through a line which leads to snow nozzle means having orifice means biased to a closed position and expanding said high pressure liquid CO through the orifice means in the snow nozzle means to create CO snow and applying said CO snow to the material being cooled and halting said creation of CO snow by applying a source of C0 vapor to the snow nozzle means at a pressure above the pressure at which the orifice means is biased to close and above the pressure at which said liquid CO is then being supplied to halt the flow of liquid CO and to create a flow of CO vapor through the orifice means.

16. A method in accordance with claim 15 wherein the pressure of said liquid CO being supplied to the snow nozzle means is reduced below a certain pressure at which CO vapor is continuously available so CO vapor is automatically applied to the snow nozzle means at said certain pressure, said certain pressure being above the pressure at which said orifice means is biased to close.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 815 377 D June 11, 1974 Inventor(s) Lewis Tyree, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 25, delete ",may be set to supply (10 vapor to" and substitute -leading to the tees 141a and l4lb.-=

Column 7, line 42, delete "toward" I v and substitute --outward Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON. JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents powso USCOMM-DC scan-P69 U.$. GOVERNMENT PRINTING QFFICE I969 0-356-384, 

1. A method for cooling material using carbon dioxide, which method comprises supplying high pressure liquid C02 through a line which leads to snow nozzle means having orifice means biased to a closed position and expanding said high pressure liquid C02 through the orifice means in the snow nozzle means to create C02 snow and applying said C02 snow to the material being cooled, halting said creation of C02 snow by reducing the pressure of said high pressure liquid C02 being supplied to the snow nozzle means below that pressure at which the orifice means is biased to close, and automatically applying C02 vapor to the snow nozzle means upon said reduction in liquid pressure and maintaining C02 vapor flow through the orifice means.
 2. A method in accordance with claim 1 wherein said C02 vapor is applied at a pressure of at least about 80 p.s.i.a.
 3. A method in accordance with claim 1 wherein the supply of liquid C02 is halted by closing valve means in the line leading to the snow nozzle means and said C02 vapor is immediately applied to the line between the valve means and the orifice means before the pressure therein can drop to about 75 p.s.i.a. to flush liquid C02 therefrom.
 4. A method in accordance with claim 1 wherein the snow nozzle means is mounted within means defining an enclosure, wherein the material being cooled is moved through the enclosure and wherein C02 vapor is caused to flow through the orifice means into the enclosure in an amount sufficient to preclude the entry of ambient air into the enclosure.
 5. Apparatus for cooling material using C02 snow, which apparatus comprises snow nozzle means having an orifice through which high pressure liquid C02 is expanded to create C02 snow and vapor, said snow nozzle means having plug means which is biased to physically close said orifice when the pressure of liquid CO2 at said snow nozzle means drops to a predetermined minimum value, means locating said snow nozzle means within an insulated enclosure into which material to be cooled is supplied by conveying means so the CO2 snow created is deposited upon the material being cooled, first conduit means for connecting said snow nozzle means to a source of high pressure liquid C02, first valve means disposed in said conduit means effective to isolate said snow nozzle means from said liquid C02 source, means for operating said first valve means to halt the creation of C02 snow, second conduit means for connecting a source of C02 vapor to said first conduit means at a location between said first valve means and said orifice, and check valve means in said second conduit means for automatically and immediately supplying C02 vapor to said first conduit means between said first valve means and said orifice upon halting of C02 snow creation to remove liquid C02 therefrom by flushing with C02 vapor.
 6. Apparatus in accordance with claim 5 wherein said second conduit means contains pressure-regulator means set to supply C02 vapor at a pressure above said predetermined minimum pressure but below the lowest pressure at which liquid C02 will be supplied to said nozzle means during snow-making.
 7. Apparatus in accordance with claim 5 wherein said orifice-plug means combination does not seal completely and permits a slow passage of C02 through said orifice when said plug means is in closed position.
 8. Apparatus in accordance with claim 5 wherein said snow nozzle means is mounted within means defining an enclosure for cooling the material, wherein means is provided for moving the mateRial to be cooled through said enclosure and wherein pressure-regulator means connected to said second conduit means supplies C02 vapor at pressure to introduce a sufficient amount of C02 vapor into said enclosure to preclude the entry of ambient air into said enclosure.
 9. Apparatus in accordance with claim 8 wherein means is provided for sensing the temperature within said enclosure, wherein said first valve means is a pressure regulating valve, and wherein control means is provided connecting said sensing means and said first valve means for changing the pressure of the liquid C02 supplied to said snow nozzle means in response to the temperature sensed within said enclosure.
 10. Apparatus in accordance with claim 5 wherein said second conduit means supplies C02 vapor at a pressure of at least about 80 p.s.i.a.
 11. Apparatus in accordance with claim 10 wherein said second conduit means includes a gas accumulator for holding C02 vapor, said check valve means being disposed between said accumulator and said first conduit means.
 12. Apparatus in accordance with claim 11 wherein said second conduit means includes second valve means between said accumulator and said source of C02 vapor, and wherein control means is provided for closing said first and second valve means at the same time when it is desired to halt snow-making.
 13. Apparatus for cooling material using CO2 snow, which apparatus comprises snow nozzle means having an orifice through which high pressure liquid CO2 is expanded to create CO2 snow and vapor, plug means for automatically closing said orifice to flow of CO2 therethrough when the liquid CO2 pressure at said snow nozzle means reaches a predetermined minimum value, means locating said snow nozzle means so the CO2 snow is deposited upon material being cooled, first conduit means for connecting said snow nozzle means to a source of high pressure liquid CO2, first valve means disposed in said conduit means effective to reduce the pressure of the high pressure liquid CO2 below said predetermined minimum pressure to thereby halt the creation of CO2 snow, second conduit means for connecting a source of CO2 vapor to said snow nozzle means, and means for automatically supplying CO2 vapor to said snow nozzle means in fluid communication with said orifice at the time of halting the CO2 snow creation.
 14. Apparatus in accordance with claim 13 wherein said snow-nozzle means is mounted within an insulated enclosure for cooling the material and wherein means is provided for moving the material to be cooled through said enclosure.
 15. A method for cooling material using carbon dioxide, which method comprises supplying high pressure liquid CO2 through a line which leads to snow nozzle means having orifice means biased to a closed position and expanding said high pressure liquid CO2 through the orifice means in the snow nozzle means to create CO2 snow and applying said CO2 snow to the material being cooled and halting said creation of CO2 snow by applying a source of CO2 vapor to the snow nozzle means at a pressure above the pressure at which the orifice means is biased to close and above the pressure at which said liquid CO2 is then being supplied to halt the flow of liquid CO2 and to create a flow of CO2 vapor through the orifice means.
 16. A method in accordance with claim 15 wherein the pressure of said liquid CO2 being supplied to the snow nozzle means is reduced below a certain pressure at which CO2 vapor is continuously available so CO2 vapor is automatically applied to the snow nozzle means at said certain pressure, said certain pressure being above the pressure at which said orifice means is biased to close. 